Computed Tomography Notes PDF

COMPUTED TOMOGRAPHY DEFINITION BRIEF HISTORY COMPUTED TOMOGRAPHY 1930’S – ALLESANDRO VALLEBONA  Creation of a cross-sectional tomographic  Proposed a m...

COMPUTED TOMOGRAPHY DEFINITION BRIEF HISTORY COMPUTED TOMOGRAPHY 1930’S – ALLESANDRO VALLEBONA  Creation of a cross-sectional tomographic  Proposed a method to represent a single section of the body with a rotating fan beam, slice of the body on the radiographic film a detector array and computed (TOPOGRAPHY) reconstruction  Other Names: Computed Axial 1970 – GODFREY NEWBOID HOUNSFIELD Tomography (CAT), Computed Transaxial  First demonstrated the CT technique Tomography (CTAT), Computed Reconstruction Tomography (CRT), Digital 1972-1974 Axial Tomography (DAT), Body Section  First clinical CT scanners were installed Roentgenography  Greek Word: “Tomos” = slice/section; 1979 “Graphia” = describing  Hounsfield & Allan Mcleod Cormack shared the Nobel Prize in Physics CT SCANNER  Consists of an x-ray source emitting finely 1980 collimated x-ray beam and a single detector  CT scan machine became widely available both moving synchronously in a translate or rotate mode or a combination of both EMI SCANNER  1st CT scan machine  180 translation/1o rotation INTRODUCTION ACTA COMPUTERS  1st CT system that could make images of any  Used Binary System part of the body  Did not require water tank BINARY DIGIT/BIT  Can code for 2 values or 2 shades of gray which correspond to white and black PRINCIPLES OF OPERATION  8 bits=1 byte  2 bytes=1 word CONVENTIONAL/AXIAL TOMOGRAPHY  16 bits=1 word  Plane of the image is parallel to the long axis of the body STORAGE REQUIREMNENT  Produces sagittal and coronal images  Kilobytes, megabytes, gigabyte or terabytes COMPUTED TOMOGRAPHY  Plane of image is perpendicular to the long axis of the body  Produces a transverse image 1  COMPUTED TOMOGRAPHY CT IMAGE 2ND GENERATION  A transaxial/transverse image  Has a narrow fan beam and multiple detectors TRANSLATION/SWEEP  It refers to movement of source-detector 3RD GENERATION assembly across the patient  Has a wide fan beam  Results in a projection  Projection: represents the attenuation 4TH GENERATION pattern of patient profile  Equipped with a detector ring  Detector signal: has a dynamic range of 12 bits (4096 gray levels) 5TH GENERATION  The electron beam tomography CT PROJECTION  An intensity profile 6TH GENERATION  The helical (or spiral) CT scanner ALGORITHM  Computer-adapted mathematical calculation 7TH GENERATION applied to raw date during image  The multi-detector row CT. reconstruction SEVEN GENERATIONS RECONSTRUCTION  Creation of an image from date FIRST GENERATION  A demonstration project RECONSTRUCTION TIME  Characteristic: translate/rotate (Bushong )  Time needed for the computer to present a or rotate/translate (Reveldez) digital image after an examination has been  X-ray Beam Shape: pencil beam computed  Detector: single detector  Time between the end of imaging and the  Imaging Time: 5-minute imaging time appearance of an image SECOND GENERATION  Characteristic: translate/rotate (Bushong ) GENERATIONS OF COMPUTED or rotate/translate (Reveldez) TOMOGRAPHY  X-ray Beam Shape: narrow fan beam  Detector: multiple detector (5-30) GENERATION OVERVIEW  Imaging Time: 30 seconds  Advantage: speed 1ST GENERATION o Rationale: consist of multiple  Has a pencil beam and one detector detectors  Disadvantages: o Increased scattered radiation 2  COMPUTED TOMOGRAPHY o Increased radiation intensity toward rotation of the x-ray source, proving a self- the edges of the beam calibrating system. Third generation system are  Compensation: used of bow- calibrated only once every few hours. tie filter  Bow-tie Filter: equalize the radiation FIFTH GENERATION (early 1980’s) intensity that reaches the detector array  Electron beam CT  Ultrafast CT scanner THIRD GENERATION  X-ray tube rotation is mechanical  Characteristic: rotate/rotate  No moving parts  X-ray Beam Shape: wide fan beam  Electron Gun: produces a focused electron  Detector: curvilinear detector array (30) beam that generates a rotating x-ray fan  Imaging Time: